Traditional semiconductor integrated circuit technology is used to integrate various electronic circuits onto a common semiconductor substrate to form a system, or subsystem. However, the traditional approach to integrating circuits into a system has process, manufacturing and design limitations which make integrating some electronic circuitry onto a common semiconductor substrate impractical. A new integration technology, namely, system-in-package (SiP) technology, attempts to overcome the limitations of the traditional approach by interconnecting multiple discrete semiconductor systems on a common substrate and encapsulating the complete system in a common package. Generally, SiP enables the integration of a mix of technologies into one package that would otherwise be difficult and expensive using the traditional approach. For example, SiP technology has been successfully applied in mixed signal applications, such as RF/wireless applications and sensor applications, as well as in networking and computing applications, and other high speed digital applications.
As previously mentioned, the multiple discrete systems of a SiP are electrically coupled together to form a system and, as is well known in the art of digital electronics, many of the multiple systems communicate with one another by transmitting digital information in the form of electrical signals. Typically, even analog based systems included in the SiP have the analog signals converted into the digital domain. The electrical signals transmitted between the multiple systems represent a serial data stream where the data is represented as binary symbols having discrete levels of amplitude or phase, as well known. Multiple electrical signals are transmitted in parallel to transmit data of a data width, with each signal representing one bit of the width of data. In transmitting the data, the electrical signal is often distorted by various phenomena, such as noise, signal strength variations, phase shift variations, and the like. Additionally, in a SiP device, where multiple individual devices interact, the various devices may operate in different voltage domains and potentially cause electrical currents to flow from one system to another. Not only do the currents result in unwanted current (i.e., power) consumption, in some cases the current may be great enough to cause damage to one of the devices.
In response, SiP devices have employed capacitively coupled signaling between the multiple systems to filter noise from the electrical signals and also prevent current flow between devices operating in different voltage domains. FIG. 1 illustrates a capacitively coupled signaling system having a capacitively coupled data bus 110 n-bits wide that is used to transmit data signals D_OUT0-D_OUTn. The data bus 110 includes output driver circuits, or transmitters 112 of the transmitting device capacitively coupled through capacitors 118 to input buffer circuits, or receivers 114 at the receiving device. The received data has been represented by the received data signals D_IN0-DINn. As shown in FIG. 1, the data bus 110 has been illustrated as a unidirectional data bus, with the transmitters 112 representing a transmitting device and the receivers 114 representing a receiving device. However, it will be appreciated that the data bus 110 has been illustrated in this manner by way of example, and that the data bus 110 can be a bi-directional data bus as well.
Lower power is consumed when utilizing capacitively coupled signaling since there is only minimal leakage current between devices. Capacitively coupled signaling is also insensitive to voltage domains, allowing operation without the need for level shifting. That is, a capacitively coupled signaling system blocks the DC component but transfers the AC component. Additionally, circuits designed for protection from electrostatic discharge are no longer necessary where the signaling is entirely contained within the SiP device. Load requirements on output circuitry can also be relaxed compared with conventional off-die signaling because the need to drive signals external to the device package are eliminated for those signals that remain internal to the SiP device.
In fabricating SiP devices, and as with other semiconductor devices, it is desirable for the individual devices to be tested to ensure that they will be operable in a SiP device before being bonded together. Otherwise, if it is determined subsequent to bonding that one of the devices will fail when operated in the capacitively coupled signaling environment, the entire SiP will need to be scrapped, or subject to rework, which subjects the remaining functional devices to greater potential for damage. Moreover, it is desirable to test a semiconductor device as it will be used in the SiP environment, that is, testing the device for functionality in a capacitively coupled signaling system by performing AC functional testing on the device.
Therefore, there is a need for a system and method for testing device that will be used in a system utilizing capacitively coupled signaling.